system
6
Pondus - yes I was using Avast 4.7 until a few weeks ago and finally updated to v6. It’s been working fine since then until yesterday. I’ve also just tried the repair option you suggested but although it showed a ‘programme updated’ status, after rebooting the same problem happened. The versions I now have are 6.0.1091. and 110418-1.
Stephen - I haven’t been using this version for 6 weeks but it could be over 30 days now. I’ve been using Avast for some years now and seem to recall getting end of 30 day trial licence reminders after updating annually but haven’t received any such notification or reminder that I need to renew it this time. Anyway I will look into that now and see if that’s the problem.
Thanks so far. 
Update: I just checked the registration details and they confirm the product is registered - it was installed 24/03/11 and is registered until 23/03/12. Although in the registration help section it mentions a 30 day requirement to confirm/register to continue to receive definition updates I haven’t actually done that yet and can’t do so because the system says I’m already fully registered ???